Arcade Collecting > Restorations & repair
Galaxian Restore
SirPeale:
I don't have any pictures of the cabinet yet, but it's dirty and rusty. It was sitting in a barn for a number of years, just like all the other restos I'm doing right now.
I don't have any room @ my house currently for the cab, but I knew the board has issues. Since the converted Galaxian cab in my boys room still has the factory harness I knew I could use that to at least display video. We'll refer to this as BOARD 1
I'll doubly document the repairs on another Galaxian board I have. I bought it several years ago from a BYOAC member. We'll refer to this one as BOARD 2.
BOARD 1 had serious problems. The corrosion I talked about? Definitely on the board too. The program ROMs I thought were just a bit rusty...nope. Removed the ROMs to find legs missing and a lot of other legs just fell off. Yikes. Good news is that the ones on the other board are just fine. So I've been swapping them back and forth between the boards when I try something.
Removed the old corroded sockets from BOARD 1 and replaced. Now I have the beginning of the startup sequence come up for just a second, with a red lined screen. I can make out "BAD RAM #1" in the flashes. I know that means I have to replace the 2114 RAM. I already replaced the 245s. I don't have sockets or RAM on hand right now, so that'll have to wait until I get them.
BOARD 2 is also problematic. It appears to not be able to sync correctly. According to the Galaxian Troubleshooting guide I should check out the IC @ 6H. I really need to learn how to use my logic probe correctly. The first time I used it only the green light would flash, but not on all the legs. The second time I got both red and green to flash on all the leads, but one set read completely different from the rest. Theorizing that the chip was bunk I cut it out, replaced it with a socket and cannibalized a replacement from a junk board. It comes up with exactly the same result, so my problems lie elsewhere. :(
I've tried tracing it out on the schematics, but can only find three of the four addresses on the schematics. Of course, this may not even be the problem! I've attached a picture.
SirPeale:
I cut out the 2114 on BOARD 1 and replaced with sockets. I popped in some 2114 I scavenged off a Pac-Man parts board (since it's all I have at the moment) and powered up. Came up with garbage, lots of flashing characters. I double checked my work, found an apparent solder bridge between two pins, and fixed that. I knew the Z80 had a broken pin (that I soldered on a temp replacement) and since I had a replacement I swapped it out.
This time it came up yet again with "BAD RAM #1". But no flashing "BAD RAM #2" in between.
I triple checked my work, making sure my solder joints were sound. They are.
I removed the 245 for giggles to see what it would do, and suddenly I had starfield generation with a garbage screen, but it kind of looked like it was running attract. Swapped that out with another and back to the "BAD RAM #1" screen. Humph. Now what?
SirPeale:
Back to BOARD 2. Since I have a Galaxian board with working sync, I was able to swap back and forth a couple times to check difference.
Pin 6 on 6H is where the composite sync comes out. If I'm reading the schematics correctly it gets the VSYNC from pin 5 of 6F, a 7474. I can't tell where it's getting the HSYNC from. The schematics merely state that comes from the HRDWR CONTROL BUS, but I'm having trouble figuring that part out. Any nudges in the right direction?
channelmaniac:
That pic doesn't look like a sync problem but more like a problem with one of the 74161 chips.
SirPeale:
--- Quote from: channelmaniac on May 31, 2009, 09:34:04 pm ---That pic doesn't look like a sync problem but more like a problem with one of the 74161 chips.
--- End quote ---
If I remove all the EPROMs I should get a solid white screen, but I get a screen that's out of sync. Also if I compare the outputs of pin 6 of 6H on BOARD 1 and BOARD 2, they're completely different. On BOARD 2, with the logic probe, both lights flash simultaneously. On BOARD 1 the flashes alternate.
I guarantee there are other problems than just sync, but I'm trying to tackle one problem at a time.
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